Embryonic Xenopus muscle cells grown in culture develop discrete patches of high acetylcholine receptor (AChR) density. By following identified muscle cells after staining with fluorescent alpha-bungarotoxin, we have found that many of these AChR patches survive in a fixed position for several days. For AChR patches on the lower surface of the cell (the surface apposed to the culture dish), mor...

The rate constants of acetylcholine receptor channels (AChR) desensitization and recovery were estimated from the durations and frequencies of clusters of single-channel currents. Diliganded-open AChR desensitize much faster than either unligandedor diliganded-closed AChR, which indicates that the desensitization rate constant depends on the status of the activation gate rather than the occupan...

The cellular mechanisms of degradation of a transmembrane protein, the acetylcholine receptor (AChR), have been examined in a mouse muscle cell line, BC3H-1. The halftime of degradation of cell surface receptors labeled with [125I] alpha-Bungarotoxin ([125I] alpha-BuTx) is 11-16 h. Leupeptin, a lysosomal protease inhibitor, slows the degradation rate two- to sixfold, depending on the concentrat...

Specific isoforms of laminin (LN) are concentrated at neuromuscular junctions (NMJs) where they may participate in synaptic organization or function. In myotubes from C2 cells, LN is concentrated within the majority of spontaneous acetylcholine receptor (AChR) aggregates. Neural agrin substantially increases this colocalization, suggesting that agrin can recruit LN into AChR aggregates. Additio...

BACKGROUND Arthrogryposis multiplex congenita (AMC) is defined as nonprogressive congenital contractures that generally result from lack of fetal movement in utero. AMC is a feature of many congenital disorders caused by genetic, environmental, or other factors. One rare cause of AMC is maternal myasthenia gravis (MG). This is an autoimmune disorder, caused by antibodies to the nicotinic acetyl...

We examined the effects of denervation on clusters of nicotinic acetylcholine receptors (AChRs) on autonomic neurons in the frog heart using immunofluorescence techniques and laser scanning confocal microscopy. We showed previously that normally innervated neurons have both large, brightly stained AChR clusters and small, dim AChR clusters. A majority (80%) of the large/bright AChR clusters are...

Neuromuscular junctions (NMJs) normally form in the central region of developing muscle. In this process, agrin released from motor neurons has been considered to initiate the formation of synaptic acetylcholine receptor (AChR) clusters (neurocentric model). However, in muscle developing in the absence of nerves and thus of agrin, AChR clusters still form in the muscle center. This raises the p...

At the neuromuscular junction, aggregates of acetylcholine receptors (AChRs) are anchored in the muscle membrane by association with rapsyn and other postsynaptic proteins. We have investigated the interactions between the AChR and these proteins in cultured C2 myotubes before and after treatment with agrin, a nerve-derived protein that induces AChRs to cluster. When AChRs were isolated from de...

Ascorbic acid in soluble extracts of neural tissue can account for the increase in surface acetylcholine receptors (AChR's) seen on L5 myogenic cells treated with crude brain extract (Knaack, D., and T. R. Podleski, 1985, Proc. Natl. Acad. Sci. USA., 82:575-579). The present study further elucidates the nature of the response of L5 cells to ascorbic acid. Light autoradiography showed that ascor...

Experimental autoimmune myasthenia gravis (EAMG) is an animal model for human myasthenia gravis (MG). Autoantibody-induced functional loss of nicotinic acetylcholine receptor (AChR) at the postsynaptic membrane is an important pathogenic feature of both MG and EAMG. To evaluate the extent at which the humoral immune response against AChR operates in the pathogenesis of EAMG, we immunized B cell...